Chop onions finely.

In a bowl add chicken, onions, ginger, potato starch, and salt. Mix very well.

Remove stems from Shiitake mushrooms. Sprinkle potato starch (not in the ingredient list) lightly over stem side of mushrooms. Then stuff the meat mixture in the mushrooms.

Heat a frying pan with oil at medium heat. Place mushrooms meat side down first. Cook until browned. Turn, cover, and cook for 3-4 minutes. Lower the heat, and add soy sauce, sake, mirin, and sugar. Cook for a couple of minutes.